A long-range North Korean rocket launched this morning disintegrated and plunged into the ocean shortly after lift-off.

The failure of the supposed Unha-3 rocket, which the US says was actually a long-range ballistic Taepodong-2 missile, is a major setback for the North Korean regime.

Pyongyang has admitted the controversial launch ended in failure and is investigating what caused it to fall into the sea.

There are reports the rocket broke into 20-odd pieces only minutes into its flight.

The South Korean army said the debris plunged into the Yellow Sea between 190 and 210 kilometres west of Kunsan, a city on the west coast of South Korea.

Timeline

North Korea's rocket program dates back to the 1970s, when it started experimenting with Scud missile variants.

Here are the key dates in the communist country's missile program so far.

"North Korea's rocket flew about one or two minutes before it exploded mid-air," the defence ministry said in a statement.

"We are conducting a search operation to retrieve the fallen objects."

US media reported earlier that a "larger than expected flare" was reportedly seen 90 seconds into the flight.

Japan also confirmed the rocket's failure.

"We have the information some sort of flying object had been launched from North Korea," Japanese defence minister Naoki Tanaka said.

"The flying object is believed to have flown for more than one minute and fallen into the ocean.

"This does not affect our country's territory at all."

Australia and the US condemned the launch, while Japan called it a "grave provocation" that ran foul of numerous United Nations resolutions.

"Today’s launch, in contravention of North Korea’s own assurance, is a provocative act that will set back negotiations," Australia's Foreign Minister Bob Carr said.

For the North Korean regime this was an issue about celebrating the birth of their great leader Kim Il-sung 100 years ago, it was confirming his grandson Kim Jong-un as the new heir to the throne and this was to be a technological achievement, something he could brag about to the North Korean people. He will probably still brag about it but it really has not been a success at all.

On the global stage this is a major failure but it's also a great relief for nations like Japan, South Korea and the United States which have been fearing for a long time that North Korea was developing sophisticated ballistic missile technology.

This is showing to them that it's not quite there. They're not at the stage where they could even put a warhead on this missile let alone have a missile that will go anywhere near the distance to hitting their neighbours.

North Asia correspondent Mark Willacy

A North Korean official said he had "no information" about the rocket's failure.

Pyongyang had maintained the rocket launch was aimed at putting a satellite into orbit and had threatened to "mercilessly punish" any nation that interfered.

The rocket's projected flight path was past the Philippines and over central Australia.

The launch had drawn widespread criticism due to concerns it could further the reclusive state's ability to deliver a nuclear warhead.

Japan had threatened to shoot down the rocket with missile interceptors if it strayed into Japanese territory.

Documents seen by the UK's Telegraph newspaper show the launch cost $815 million - enough money for the impoverished nation to buy 1.5 million tonnes of rice.

Security Council meeting

The UN's 15-member Security Council will meet in emergency session on Friday to discuss the launch, a UN diplomat said.

Russia's envoy to the UN, Vitaly Churkin, earlier said that all Council members agreed that a launch would be a "violation" of US sanctions resolutions imposed in 2009 after Pyongyang's last nuclear test.

US secretary of state Hillary Clinton earlier warned North Korea that if it were to go ahead with the launch, "we will all be back in the Security Council to take further action."

She said the launch would violate Security Council resolutions banning the communist state from ballistic missile activity.

"There is no doubt that this (launch) would use ballistic missile technology," she said.

Senator Carr says it is hard to say how North Korea will behave now.

"It's very hard to judge what motivates this regime; it's a one-party Marxist-Leninist dictatorship, but it could well be the case that this failure will put pressure on the leadership to do something even wilder to maintain public support with the 25 million people of North Korea."